1. Field of the Invention
The present invention relates generally to a receiving device in a CDMA (Code Division Multiple Access) communication system, and in particular, to a receiving device in a multi-carrier CDMA communication system.
2. Description of the Related Art
A single carrier is used in CDMA based on the IS-95 standards. A general CDMA rake receiver employs direct spreading and uses one carrier for each transmission path. The future CDMA communication system, however, can transmit user data simultaneously in a plurality of frequency bands in a multi-carrier scheme.
FIG. 1 is a block diagram of a multi-carrier transmitting device.
Referring to FIG. 1, a channel encoder 110 encodes input data in frame units and generates encoded symbol data. If the symbol data is not at a full rate a rate matcher 120 repeats the symbol data received from the channel encoder 100 to achieve a full rate data. An interleaver 130 interleaves the output of the rate matcher 120. Here, the interleaver 130 may be a block interleaver.
A long code generator 191 generates a long code for scrambling a received signal. The long code is different for each user to identify the individual user. A decimator 192 decimates the long code to match the symbol rate at the output of the interleaver 130. An adder 193 adds the outputs of the interleaver 130 and the decimator 192. The adder 193 can be an XOR gate.
A demultiplexer 140 sequentially demultiplexes the data received from the adder 193 with different carriers. First to third level converters 151 to 153 convert the binary data received from the demultiplexer 140 to 4-level data. The level converters 151 to 153 convert 2-level data to 4-level data. Therefore, they convert 0s and 1s of the input data to 1s and xe2x88x921s, respectively. First to third orthogonal modulators 161 to 163 orthogonally modulate data received from the corresponding first to third level converters 151 to 153 with their respective assigned orthogonal codes. The orthogonal codes can be Walsh codes. First to third PN spreaders 171 to 173, which can be complex spreaders, modulate the outputs of the first to third orthogonal modulators 161 to 163. First to third gain controllers 181 to 183 control the gains of the spread signals received from the first to third PN spreaders 181 to 183 by means of input gain control signals Ga to Gc. The signals output from the first to third gain controllers 181 to 183 are modulated with different carrier signals, prior to multi-carrier transmission.
As described above, the forward link structure shown in FIG. 1 generates three encoded symbols for one input bit in the ⅓ rate channel encoder 110 and transmits the encoded symbol data in three carriers through the rate matcher 120 and the interleaver 130. That is, the CDMA forward link structure of FIG. 1 subjects input data to encoding, interleaving, and demultiplexing and then separately transmits the resulting data in three carriers.
To accurately receive signals in different frequency bands from the transmitting device, a receiving device should demodulate the input signals in synchronization with the carrier for each transmission path.
It is, therefore, an object of the present invention to provide a receiving device for synchronizing with an input multi-carrier signal in time, frequency, and phase in a multi-carrier CDMA communication system.
It is another object of the present invention to provide a receiving device which can compensate for time delay and phase errors of an input multi-carrier signal separately for individual carriers in a multi-carrier CDMA communication system.
It is a further object of the present invention to provide a receiving device which can compensate for time delay of an input multi-carrier signal commonly for all carriers and can compensate for phase errors individually for the carriers in a multi-carrier CDMA communication system.
It is still another object of the present invention to provide a receiving device which can compensate for time delay of an input multi-carrier signal individually for the carriers and compensate for phase errors commonly for the carriers in a multi-carrier CDMA communication system.
These and other objects are achieved by providing a receiving device in a multi-carrier CDMA communication system. In the receiving device, a time compensation means has a time tracker for each of the signals received on multi-carriers and generates a time delay compensation signal by combining time errors of the carriers received from the time trackers. A first PN sequence generator generates a first PN sequence whose time delay is compensated for by the time delay compensation signal. A plurality of PN despreaders PN-despread the signals received on the multi-carriers by the first PN sequence. A frequency compensation means detects pilot signals corresponding to the PN-despread signals, generates frequency error signals for the carriers by the detected pilot signals, and compensates for frequency errors of the signals received on the multi-carriers. A phase compensation means compensates for phases errors of the carriers using the PN-despread signals and the pilot signals. A multiplexer multiplexes the phase-compensated signals.